Do-it-yourself spot welding device. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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The advantage of spot welding is indisputable when performing welding work on small parts. With the same quality of the welded joint, energy costs are reduced several times. The proposed device is indispensable for welding sheet parts up to 1 mm thick or bars, wires up to 4 mm in diameter. These parameters are determined by the geometric dimensions and thermal conductivity of the material.

Functionally, the proposed device consists of three nodes: 1 - control unit; 2- welding transformer; 3 - contact welding unit.

Main technical parameters

• Supply voltage ...... 220 V, 50 Hz
• Idle output voltage ...... 4 - 6V
• Maximum pulsed welding current ...... up to 1500 A

For the manufacture of the control unit, you will need a transformer with a power of 10 - 20 W with a mains winding voltage of 220 V, 50 kHz and a secondary winding voltage of 15 - 25 V; a set of electrolytic capacitors type K50-35; reed relay type RES42; RES43; RES55 or other electromechanical with low tripping current and operating voltage 15 - 25; switch button type KM-1 or other; block of switches type P2K with independent switching on 5-6 positions for connecting capacitors when selecting the time of the welding cycle; diode bridge for charging capacitors with constant voltage type KTs402 - KTs407; variable resistor with a power of 1 - 3 W of group A or wire.

The main part of the control unit is the MTT4K power switch - a single-phase non-contact thyristor starter for a current of 40 - 80 A and a voltage of 600-800 V, manufactured by Element-Transformer LLC (Zaporozhye).

For the manufacture of a power welding transformer T2 (Fig. 1), a magnetic circuit was taken from a faulty laboratory autotransformer for 2,5 A. Having removed the old winding, we cut out two washers from an electric cardboard with a thickness of 0,5-1,0 mm, which we put on the ends of the magnetic circuit with an overlap in 1-2 mm along the inner and outer diameters, followed by bandaging with varnished cloth or similar material for at least three layers to achieve electrical and mechanical strength that prevents destruction and rubbing of the network winding on the magnetic circuit during operation. The diameter of the network winding wire is 1,2-1,5 mm, preferably in fabric insulation for better impregnation with varnish.

We lay the wire coil to coil evenly around the entire perimeter of the magnetic circuit according to Fig. 2.

After winding the primary winding, it is bandaged with a cotton tape and impregnated with varnish of the type KS521, EP730 or similar. The secondary winding contains 4-7 turns of stranded copper wire with a diameter of at least 20 mm and a cross section of at least 300 mm2 in silicone insulation or a similar bundle. Appropriate lugs should be put on the ends of the winding, followed by soldering to achieve the minimum resistance of the contact transition. The contact welding unit is made taking into account the requirements for the technological process. The material for the electrodes can be copper, beryllium bronze and their substitutes.

To create a high-quality welding core, the contact area of ​​the electrode must be minimal, it is also necessary to ensure a snug fit and compression of the parts to be welded with a force of at least 20 kg/cm2 (this force is selected when working out the technological process).

When assembling the device, special attention should be paid to the quality of the connections in order to obtain minimal losses on the contact resistances.

Operating procedure

When the contact KN-1 or any of the switches P2K is closed, the selected capacitance C1-Cx is charged to a supply voltage of 15-30 V, and after pressing KN-1, the charge circuit opens and the discharge circuit K1 - RES is connected. The value of the capacitance, and consequently, the energy stored by it, determines the time the RES relay is kept in the closed state, i.e. welding cycle time by passing the power current through the MTT4K 80-8 power switch from several to tens of mains voltage periods. In order to reduce the number of capacitors and P2K switches for selecting the welding cycle time, they can be assembled in a parallel circuit.

Approximate ratings of capacitances C1 and C2 are 47 microfarads each, C3 and C4 are 100 microfarads each, C5 and C6 are 470 microfarads each, all capacitances are for an operating voltage of at least 30 V charging. A more accurate welding cycle time is selected with a variable resistor R2. Coarse adjustment of the welding current is carried out by switching the taps of the power transformer T2.

The MTT4K power switch (Fig. 4) is a potential-free thyristor-diode module in a unified MTTXNUMX package.

The control current flowing through the relay contacts does not exceed 100 mA.

The MTT4K power switch must be installed on a cooling radiator with an area of ​​400-600 cm2 or use the heat-removing area of ​​the device case, not forgetting that mains voltage is present on the power and control contacts.

Author: A.I. Sapronov, Zaporozhye

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